<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      .a {
        background-color: burlywood;
        height: 30px;
        width: 30px;
        float: left;
      }
      .b {
        background-color: red;
        height: 40px;
        width: 40px;
        float: left;
      }
      .c {
        background-color: blue;
        height: 50px;
        width: 50px;
        float: left;
      }
      .ff{
        height: 30px;
        width: 600px;
        background-color: brown;
      }
      .father{
        border: solid 2px green;
        /* display: flow-root; */
      }
      .father::after{
        display: block;
        content: "";
        clear: both;
      }
      /* BFC 格式化 */
    </style>
  </head>
  <body>
    <div class="father">

        <div class="a"></div>
        <div class="b"></div>
        <div class="c"></div>

    </div>
    <div class="ff">
    </div>
  </body>
</html>
